Nutritionists have stressed increasingly the need for calcium in the diet of men and woman of all ages as well as children. Recently, attention has been directed toward calcium and its role in preventing osteoporosis, the degenerative bone disease.
Niney-nine percent of the body's calcium is present in teeth and bones. Calcium is thus needed for both bone formation and maintenance. The other one percent circulates in the blood and is in part ionized. In its ionized form, calcium is of great importance in blood coagulation, in the function of the heart, muscles and nerves, and in the permeability of membranes. Calcium is also vitally important for normal nerve transmission, muscle contraction, heart function and blood clotting. If inadequate amounts of calcium reach the blood from dietary sources, calcium is removed from bones to make up the difference. Current scientific research shows evidence of calcium playing a part in protecting against high blood pressure and colon cancer.
An expert panel on bone health called together by the National Institute of Health summed it up with these words: "In some studies, high dietary calcium suppresses age-related bone loss and reduces the fracture rate in patients with osteoporosis". The U.S. Recommended Daily Allowance (R.D.A.) of calcium is 1000 mg. Many adult Americans are consuming lesser amounts of calcium. By increasing the amount of calcium in milk, it will be possible for people to more easily meet the U.S. R.D.A. for calcium. In addition, calcium is best absorbed when accompanied by vitamin D and lactose, both of which are found in milk.
Calcium-enriched food products and particularly calcium-enriched fresh milk have been developed and used from time to time in the past. However, until the development of the product and process of this invention, calcium-enriched fresh milks have had serious drawbacks. These milks have lacked stability and have had an off-taste. They have not tasted like good fresh milk. In addition, the source of calcium, usually an inorganic salt in finely divided form, has tended to settle out. This renders the calcium content non-uniform unless the milk is shaken, and forms a heavy sediment that may be difficult to re-suspend in the milk.
A canned calcium-enriched milk is described in the Bauer U.S. Pat. No. 2,871,123. Calcium carbonate was used as the calcium source and carrageenan gum for suspension. The product was a concentrated milk product which was diluted to make an infant formula.
A calcium-enriched fresh 1% butterfat milk presently sold under the trademark "CalciMilk" by Lehigh Valley Farms contains, according to the label, 66% more calcium than regular low fat milk. This product contains tricalcium phosphate to increase the calcium content, cellulose gel, and carrageenan. It also has lactase enzyme added to break down the lactose in milk. "Shake before serving" is printed on the carton, indicating that the tricalcium phosphate settles out.
The ability of different individuals to utilize the calcium in foods varies considerably. Generally, when an individual partakes of a high protein diet, about 15% of the dietary calcium is absorbed. When the individual partakes of a low protein diet, only about 5% of the dietary calcium is absorbed. Phytic acid in cereal grains interfers with calcium absorption by forming insoluble calcium phytate in the intestine. Oxalates in foods, such as spinach and rhubarb, may have a similar effect.
Other intestinal factors that influence the absorption of calcium include pH, since the more alkaline the contents of the intestines, the less soluble are the calcium salts; the calcium:phosphorus ratio, since a high ratio favors the formation of tricalcium phosphate rather than the more soluble, better absorbed forms; the presence of free fatty acids, which occurs when fat absorption is impaired; and the amount of vitamin D present, since vitamin D promotes the absorption of calcium from the intestine.
Phosphorus is found in every cell of the body, but like calcium, most of it is found in the bones and teeth. About 10% of the total phosphorus in the body is present in combination with proteins, lipids, and carbohydrates, and in other compounds in blood and muscle. Another 10% is widely distributed in a variety of chemical compounds. Phosphate ester is of great importance in energy transfer as is well known.
The metabolism of phosphorus is closely related to that of calcium. The calcium:phosphorus ratio in the diet affects the absorption and excretion of both of these elements. If either element is taken in excess, excretion of the other is increased. The optimal ratio is 1:1 when the intake of vitamin D is adequate.
Given all of this background information, it is apparent that the production of a shelf-stable, consumer-acceptable milk product fortified with added calcium and phosphorus would be an important contribution to human nutrition.